The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Current alarm safety systems (such as multi-point fire safety systems) allow users to activate an alarm signal by operating any one of a plurality of switches at different locations in a room, building, vehicle, etc. Upon operating an “activation point”, for example by pressing a switch, an electrical signal is sent via a cable to a central processing unit. Upon receipt of the electrical signal, the central processing unit emits an alarm signal, such as an audible or visible alarm signal.
There are a number of disadvantages associated with such multi-point electric safety systems. Firstly, they can be expensive and difficult to install. Also, such safety systems are not suited to certain environments. For example, there can be disadvantages when using such safety systems in dirty, for example wet, environments. Further, due to the expense of and difficulty in installing such systems, they are not suited for temporary applications.
Alarm safety systems which rely on electromagnetic signals are disclosed for example in GB-A-2128649, GB-A-2409085, GB-A-2288014, U.S. Pat. No. 5,548,275, GB-A-2186683, GB-A-2091874, GB-A-2063536, WO-A-99/38182 and U.S. Pat. No. 3,753,221.
Current safety edge systems for garage door applications use continuous contact strip metal contacts or pneumatic tubes to allow activation of the edge at all points. For copper contacts, the system detects a closed circuit and outputs accordingly. For pneumatic edges, a particular volume of air must be displaced in a sealed chamber to allow a diaphragm to close two electrical contacts.
There are a number of disadvantages to these systems which can result in poor performance. For example, an electrical safety edge that utilizes two contacts where either have ferrous content are prone to rust when seals are broken and can short out. The pneumatic edge requires an airtight seal throughout the system as the loss of pressurization when pressed will not activate the pressure diaphragm.